Why?
Unbelief, which brings about distrust
Lack of faith, which undermines confidence
Misunderstanding of the Gospel, which causes us to misunderstand our position in Christ and buy into the thinking of the world.
We distrust His promise to complete His work in other believers and ourselves.
We shrink back because we don't have confidence.
We think of ourselves as hopelessly terminal in our failings until we get to heaven.
In our minds, the power of the fullness of the Godhead has become considerably less than the power of the enemy, the world, our own flesh and the waves that buffet us.
Why?
We have withdrawn ourselves from His power.